This invention relates generally to an apparatus and to a method for processing a work piece such as a semiconductor wafer, and more specifically to an apparatus and a method for spinning a work piece such as for spin drying the work piece as a part of a manufacturing process.
This invention relates to the processing of objects that are generally in the shape of flat, circular disks. Such objects include, for example, semiconductor wafers, compact disks, memory disks, optical blanks, and the like. Without loss of generality, such objects will be referred to as xe2x80x9cwork pieces.xe2x80x9d Illustrative examples will refer specifically to the use of this invention in connection with the processing of semiconductor wafers, but such examples are presented merely to aid in understanding, and are not intended to limit in any way the generality of the invention.
During the fabrication of a work piece, the work piece may be subjected to various processing steps. In the case of fabricating a semiconductor wafer, those process steps may involve the growth or deposition of insulating layers, the deposition of metal or other conductive layers, impurity doping, photolithographic patterning, planarization, and the like. The fabrication of such semiconductor wafers requires extreme cleanliness of the wafer at various stages of the process. Accordingly, the above process steps are often preceded or followed by cleaning steps to insure that the requisite cleanliness of the wafer is maintained. The cleaning steps may involve, for example, steps such as scrubbing, spray cleaning, rinsing and the like. At the completion of the cleaning steps, the wafer is usually processed to remove any water or other cleaning agents during the cleaning operation. Such removal is necessary to prepare the wafer for the next process step and to prevent the water or cleaning agent from drying on the wafer surface and leaving a contaminating residue.
Spin drying is a process commonly used to remove liquid residue from the surface of a work piece. In such a process the work piece is spun about its axis at a high rotational velocity so that centrifugal force drives droplets of the liquid radially outward and off the work piece surface. Spin drying is accomplished by placing the work piece on a platform that is coupled to a drive motor. The drive motor causes the platform to spin at a velocity, for example, on the order of 1000-4000 rpm. The work piece must by properly positioned on the platform to insure that the work piece is not thrown from the platform during the spinning. The positioning, however, should be such that a minimum of the work piece surface is covered or touched by the positioning mechanism because the spin drying may be ineffective with respect to the covered or touched areas. In addition, the area touched by the positioning mechanism should be minimized because any clamping or other touching of the sensitive surface of the work piece may damage that surface. With semiconductor wafers, for example, the usual rule of thumb is that no clamp or other mechanism can touch any part of the wafer surface more than 3 mm beyond the edge of the wafer. Especially when using such minimal touching, care must be exercised to insure that the work piece is properly positioned before the spinning mechanism is engaged. Spinning a work piece that is misaligned may cause work piece breakage.
As the processing of work pieces becomes ever more exacting, the need for better and better cleaning processes becomes more important. For example, in the semiconductor industry, the size of the features of a semiconductor device is shrinking with every new generation of devices. At the same time, the spacing between devices is shrinking. With smaller features and closer spacing, wafer cleanliness becomes of supreme importance. Even tiny particles or contaminates can adversely affect device performance or can even cause device failure. In addition to the necessity of producing a clean, contamination free product, however, it is highly desired that the cleaning and drying processes should be fast and efficient. Preferably such process should be highly automated. Although spin drying is now widely practiced in the processing of work pieces such as semiconductor wafers, the presently available apparatus and processes are somewhat lacking in providing a highly automated, efficient cleaning with minimal but reliable contacting of the work piece surface.
Accordingly, a need exists for a work piece spinning apparatus and method that overcomes the deficiencies attendant with present apparatus and its use. Although such apparatus is particularly applicable for spinning a work piece in a spin drying process, the apparatus can also find application in other work piece spinning processes such as the spin application of a process chemical to the surface of the work piece or the spin rinsing of the work piece surface.